This invention relates to paperboard coated so that browning is minimized when the paperboard is subjected to temperatures of up to about 205.degree. C. (400.degree. F.). It also relates to methods for minimizing such browning by applying certain coatings to the paperboard.
It is common practice to package convenience foods in disposable cooking or heating utensils which also can, if desired, serve as an eating receptacle or plate. Until the advent of microwave ovens for use in home kitchens, the most common containers for convenience foods to be heated within the container were formed of thin sheet aluminum or layers which included aluminum foil. However, because aluminum cannot generally be used in microwave cooking--and, also, because of the relatively high cost of aluminum as opposed to paperboard--paperboard containers for such convenience foods have become increasingly popular.
Convenience foods may, for example, be precooked and packaged in containers and then reheated. The containers in which such foods are packaged must therefore be capable of withstanding the food heating operation without causing any adverse effects on the food or the package itself. The containers, therefore, must be capable of being subjected to temperatures of up to about 176.degree.-205.degree. C. (about 350.degree.-400.degree. F.) Furthermore, since many convenience foods are frozen, the container must also be able to withstand low temperatures in the range of about -24.degree. C. (about -10.degree. F.). Paperboard containers for such food products coated with various polymeric plastic substances are well known in the art and, in many instances, such containers are able to withstand these high and low temperatures. For example, U.S. Pat. No. 3,813,256 discloses food heating utensils comprising paperboard coated with polyphenylene oxide or polysulfones. U.S. Pat. No. 3,904,104 and U.S. Pat. No. 4,147,836 disclose such paperboard products coated with polypropylene or polyester.
Despite the wide spread use of coated paperboard in the food packaging industry, there remains the problem of paperboard browning at temperatures exceeding about 150.degree. C. (302.degree. F.). Although such containers may retain their utilitarian function despite the browning, there are obvious esthetic disadvantages, particularly when the container is also intended for use as an eating utensil.